Electrode fixation in interventional medical systems

ABSTRACT

An implantable medical device assembly includes a mounting structure, an electrode, and fixation tines. The electrode protrudes from a surface of the structure, offset proximally from a distal end of the structure, and approximately centered between first and second sides of the structure. Each tine extends away from the surface—a first adjacent the first side, and a second adjacent the second side. Each tine is elastically deformable from a relaxed condition, in which the tine extends toward a proximal end of the structure, to an extended condition, in which the tine extends away from the distal end of the structure. A delivery tool has first and second longitudinally extending sidewalls to receive passage of the structure therebetween. When the structure distal end is located between proximal ends of the sidewalls, a rail-like edge of each sidewall receives, and elastically deforms to the extended condition, a corresponding tine.

CROSS-REFERENCE TO RELATED APPLICATION

The instant application is related to the co-pending and commonlyassigned United States patent application entitled, ELECTRODE FIXATIONIN INTERVENTIONAL MEDICAL SYSTEMS, having the Ser. No. 15/287,122(Attorney Docket No.: C00010730.USU1), which was filed on Oct. 6, 2016,and is hereby incorporated by reference.

TECHNICAL FIELD

The present invention pertains to interventional medical systems, and,more specifically, to implantable electrode fixation at a stimulationsite.

BACKGROUND

An implantable medical device, for the delivery of stimulation therapy,may include an electrode and a fixation component configured to hold theelectrode in intimate contact with tissue at a stimulation site. Onetype of such a device may be an implantable cardiac pacemaker thatincludes a pulse generator and a pacing electrode coupled to thegenerator, for example, by an elongate insulated lead wire. A pacingsite may be located on an epicardial surface of the heart, for example,on the left side of the heart for the application of pacing therapy totreat heart failure. FIG. 1 is a schematic showing an access site A forcreating a passageway between a patient's diaphragm 19 and xiphoidprocess 20 of sternum 13, for example, to implant a pacing electrode onan epicardial surface 6 of the patient's heart, which is enclosed withinthe pericardial sac 15. After making a superficial incision, an operatormay open a passageway between diaphragmatic attachments 18 and diaphragm19 by using blunt dissection tools and techniques that are known in theart. Then, the operator may employ a piercing tool to pass a guide wirethrough the pericardial sac 15, also according to methods known in theart. The operator may use fluoroscopic guidance to position a distalportion of the guide wire along a portion of epicardial surface 6, atwhich a target site is located, and then pass a guiding sheath over thepositioned guide wire. The guiding sheath then serves as a conduit fordelivery of the implantable electrode to the target site. In thiscontext, to deliver and then fix, or secure the implantable electrode atan epicardial site, there is a need for new configurations ofinterventional systems and associated implantable device assemblies.

SUMMARY

An implantable medical device assembly, according to some embodiments,includes a mounting structure, an electrode, and first and secondtissue-penetrating fixation tines; wherein the electrode protrudes froma surface of the structure at a location that is offset proximally froma distal end of the structure and is approximately centered betweenfirst and second sides of the structure, and wherein a segment of eachfixation tine extends away from the surface of the structure, the firstfixation tine segment, at a location adjacent the first side and distalend of the structure, and the second fixation tine segment, at alocation adjacent the second side and distal end of the structure. Eachtine segment is elastically deformable from a relaxed condition to anextended condition; wherein, in the relaxed condition, each tine extendstoward a proximal end of the mounting structure so that a piercing tipof each tine is located adjacent to the electrode, and, in the extendedcondition, each tine extends away from the distal end of the mountingstructure, so that each piercing tip is located distal to the distal endof the mounting structure.

In some embodiments, each fixation tine is a component formed from asuper-elastic wire, and the component may include a mounting segment(e.g., pre-formed in an L-shape), and the above-described segment (e.g.,pre-formed in a V-shape), which extends from the surface of the mountingstructure and is terminated by the piercing tip. The segments may bendtoward one another, in a single plane, the same for both. In the abovedescribed assembly, the mounting structure may include first and secondchannels that extend lengthwise, between the proximal and distal ends ofthe structure, wherein the mounting segment of each fixation tineextends a corresponding channel.

An interventional medical system, according to some embodiments,includes the above described device assembly and a delivery tool, whichhas first and second longitudinally extending sidewalls spaced apartfrom one another to receive passage of the assembly mounting structuretherebetween, so that, when the structure is passed therebetween, untilthe distal end thereof is located between proximal ends of thesidewalls, a rail-like edge of each sidewall receives in engagementtherewith, and elastically deforms to the extended condition, acorresponding fixation tine segment. According to some methods, after anoperator positions the holding member and the device assembly, with thefixation tines in the extended condition, at an epicardial site, theoperator releases the fixation tines from the extended condition, toengage with tissue at the site, by applying a push force to the mountingstructure of the device assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments of thepresent invention and therefore do not limit the scope of the invention.The drawings are not to scale (unless so stated) and are intended foruse in conjunction with the explanations in the following detaileddescription. Embodiments will hereinafter be described in conjunctionwith the appended drawings wherein like numerals/letters denote likeelements, and:

FIG. 1 is a schematic depicting a sub-sternal access site through whichan implantable electrode may be passed for securing to an epicardialsurface of a patient's heart;

FIGS. 2A-C are various plan views of an implantable medical deviceassembly, according to some embodiments;

FIGS. 3A-B are a plan view and a cross-section view of atissue-penetrating tine component, according to some embodiments;

FIG. 4A is a plan view of an interventional medical system, according tosome embodiments, that includes a delivery tool together with the deviceassembly of FIGS. 2A-C;

FIG. 4B is an end view of the system, according to some embodiments;

FIG. 4C is a perspective view of a portion of the system, according tosome embodiments;

FIG. 5 is a schematic showing the delivery tool positioned for securingan electrode of the medical device assembly at an epicardial site,according to some methods; and

FIG. 6 is a schematic depicting release of tissue-penetrating fixationtines in the interventional medical system, according to someembodiments.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is notintended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the following description providespractical examples, and those skilled in the art will recognize thatsome of the examples may have suitable alternatives.

FIGS. 2A-B are plan views, from different perspectives, of animplantable medical device assembly 300, according to some embodiments.A mounting structure 310 of device assembly 300 is shown having a lengthdefined from a proximal end 31P to a distal end 31D thereof, a thicknessdefined from a first surface 311 to a second surface 312 thereof, and awidth defined from a first side 301 to a second side 302 thereof. FIGS.2A-B illustrate assembly 300 including an electrode 32 protruding fromfirst surface 311 of structure 310 at a location offset proximally fromstructure distal end 31D and approximately centered between first andsecond sides 301, 302. According to some exemplary embodiments,structure 310 may be formed from a biocompatible and biostableinsulative polymer, such as silicone, or urethane, or a combinationthereof. FIGS. 2A-B further illustrate first and secondtissue-penetrating fixation tines 341, 342 of assembly 300 being locatedon either side of electrode 32, wherein first tine 341 extends fromsurface 311 of structure 310 at a location adjacent to first side 301and distal end 31D, and second tine 342 extends from surface 311 at alocation adjacent to second side 302 and distal end 31D. Each tine 341,342 includes a tissue-piercing tip 40, and FIGS. 2A-B show tines 341,342 in a relaxed condition, bending toward proximal end 31P and firstsurface 311 of structure 310, so that each piercing tip 40 is locatedadjacent to electrode 32. According to preferred embodiments, each tine341, 342 is formed from a super-elastic material and includes apre-formed V-shaped segment 4V configured to secure electrode 32, inintimate tissue contact, at a stimulation site on an epicardial surfaceof a patient's heart. Electrode 32 may be constructed from any suitablematerial and by any suitable method known to those skilled in the art ofmedical electrical cardiac pacing.

Pre-formed V-shaped segment 4V of each fixation tine 341, 342 iselastically deformable from the illustrated relaxed condition, which isthat of the pre-formed V-shape, to an extended condition, in which eachsegment 4V extends distally away from distal end 31D of structure 310,so that tips 40 are located distal to structure distal end 31D, forexample, as described below in conjunction with FIG. 4A. Tines 341, 342may be held in the extended condition until an operator positionsassembly 300 in proximity to a stimulation site, after which theoperator may release tines 341, 342 from the extended condition so thatpiercing tips 40 ‘bite’, or penetrate into tissue adjacent the site,thereby securing electrode 32 in intimate tissue contact for stimulationtherapy.

With reference to FIG. 2A, in conjunction with FIG. 2C, which is anotherplan view of device assembly 300, each tine 341, 342 may be secured tostructure 310 by a pre-formed L-shaped segment 4L thereof (dashed linesin FIG. 2A). FIG. 2C illustrates each L-shaped segment extending in acorresponding channel 318 of mounting structure, being interlockedtherewith, and, for example, further secured thereto by a backfill of amedical grade adhesive material, according to some embodiments.According to the illustrated embodiment, each channel 318 extendsthrough structure 310, from first surface 311 toward second surface 312and then lengthwise adjacent to a corresponding side 301, 302 ofstructure 310. However, according to alternate embodiments, in which themeans for mounting tines 341, 342 is varied, what is herein designatedas the L-shaped segment 4L of the illustrated embodiment can bepre-formed into any other suitable shape that conforms to alternatemounting means.

FIG. 3A is a plan view of either of tissue-penetrating fixation tines341, 342 as a separate component from assembly 300, according to someembodiments. FIG. 3A illustrates tine 341, 342 including theaforementioned pre-formed L-shaped and V-shaped segments 4L, 4V, whereinL-shaped segment 4L extends from a first end 4L1 thereof to a second end4L2 thereof around a bend that encloses a 90 degree angle, and V-shapedsegment 4V extends from second end 4L2 of L-shaped segment 4L topiercing tip 40, and bends toward L-shaped segment 4L. FIG. 4A furtherillustrates V-shaped segment 4V including a first, relatively straight,portion 4V-1, a second, arched, portion 4V-2, and a third, relativelystraight, portion 4V-3, wherein second portion 4V-2 connects first andthird portions 4V-1, 4V-3, and third portion 4V-3 is terminated bypiercing tip 40. A length of third portion 4V-3, for example, about 0.12inch, sets a depth to which each tine 341, 342 can penetrate into tissueat an implant site; and a length of second portion 4V-2, for example,about 0.08 inch around a radius of about 0.03 inch, adds a bit of depthto the penetration and determines how much tissue is encompassed by thepenetrating tines 341, 342. The release of tines 341, 342 for ‘biting’is described in greater detail below, in conjunction with FIG. 6.

FIG. 3B is cross-section view of tine 342, through section line B-B ofFIG. 3A, and, with reference to FIG. 3B in conjunction with FIG. 3A,each tine component 341, 342 has a generally rectangular axialcross-section that is uniform along both segments 4L, 4V, sans piercingtip 40, wherein a single plane in which both segments 4L, 4V bend isorthogonal to longer sides of the axial cross-section. According to anexemplary embodiment, tine components 341, 342 may be formed from arolled Nitinol wire (e.g., having a diameter of approximately 0.012inch, prior to rolling), and piercing tip 40 is formed by a first angledsurface cut in one of the longer sides of the axial cross-section,according to an angle π (FIG. 3A), for example, of about 25 degrees.Each of tine components may also include a second angled surface cutinto one of the shorter sides of the axial cross-section, according toan angle β (FIG. 3B), for example, of about 60 degrees, wherein, withfurther reference to FIG. 3B, in conjunction with FIG. 2B, the secondangled surfaces of tines 341, 342 face generally toward one another inassembly 300, such that the dashed line in FIG. 3B represents the secondangled surface of tine 341.

With further reference to FIGS. 2A-B, when device assembly 300 forms animplantable medical electrical lead, assembly 300 further includes anelongate conductor that is coupled to electrode 32 (dashed line in FIG.2B), and an elongate insulation body 210 that is joined to mountingstructure 310 and extends around the conductor to provide electricalisolation. According to the illustrated embodiment, the conductorextends proximally from proximal end 31P of structure 310 and withininsulation body 210 to a connector subassembly 215, which is configuredfor coupling to an implantable pulse generator, such as a pacemaker (notshown). FIG. 2B further illustrates device assembly including one ormore optional additional electrodes 35, 36 and corresponding insulatedconductors (dashed lines) coupled thereto. Optional electrode 35 isshown mounted to surface 311 of structure 310, for example, for bipolarfunction with electrode 32, according to some embodiments; alternately,electrode 35 can be mounted opposite electrode 32, to second surface 312of mounting structure 310. Optional electrode 36 is shown mounted to anelongate insulation body 610 that extends distally from distal end 31Dof mounting structure 310, and through which the corresponding conductor(dashed line) extends. According to an exemplary embodiment thatincludes electrode 36, electrode 36 may be spaced apart from electrode32 by a distance of about one to two inches, for example, to create a‘wide’ dipole for atrial sensing. A construction of the conductor(s),insulation body 210 (and optional body 610), and connector subassembly215 of assembly 300, as well as of the pulse generator, may be accordingto any suitable means known to those skilled in the art of implantablemedical stimulation systems.

FIGS. 4A-B are a plan view and an end view of an interventional medicalsystem, according to some embodiments, that includes a delivery tool 500together with device assembly 300; and FIG. 4C is perspective view of aportion of the system, according to some embodiments. FIGS. 4A-Cillustrate device assembly 300 received between first and secondlongitudinally extending sidewalls 531, 532 of a holding member 530 ofdelivery tool 500, which holding member 530 is attached to a distal endof an elongate shaft 510 of tool 500. FIGS. 4B-C illustrate sidewalls531, 532 being spaced apart from one another, to receive passage ofdevice assembly 300 therebetween, and each sidewall 531, 532 including arail-like edge 531E, 532E. With further reference to FIGS. 4A and 4C,each sidewall 531, 532 extends over a length defined from a proximal end531P, 532P thereof to a distal end 531D, 532D thereof, and edges 531E,532E extend along the length. According to the illustrated embodiment,each sidewall edge 531E, 532E is sized to receive in engagementtherewith, and to elastically deform, from the relaxed condition to theextended condition, V-shaped segment 4V of a corresponding fixation tine341, 342, when proximal end 31P of device assembly mounting structure310, with surface 311 facing toward edges 531E, 532E, is passed betweensidewalls 531, 531 (e.g., per arrow L), from distal ends 531D, 532Dthereof to proximal ends 531P, 532P thereof, and then proximally beyond.(Dashed lines in FIG. 4A depict distal end 31D of mounting structure 310between holding member sidewalls 351, 352, and the extended condition oftines 341, 342, being engaged in edges 351E, 352E.) Thus, an operatormay employ tool 500 to position device assembly 300, with tines 341, 342in the extended position, at an epicardial site.

According to some embodiments, holding member 530 further includes meansfor engaging device assembly mounting structure 310, in proximity toproximal end 31P, when distal end 31D is located between holding membersidewalls 531, 532, to prevent distal end 31D from passing proximallyout from between sidewalls 531, 532. FIGS. 4A and 4C illustrate thismeans being first and second stop members 535A, 535B that extendproximally from respective sidewall proximal ends 531P, 532P, and areoriented to abut respective first and second sides 301, 302 of mountingstructure 310, for example, by extending inward toward one another, asbest seen in FIG. 4C. Furthermore, with reference to FIGS. 2B-C, inconjunction with FIG. 4C, mounting structure sides 301, 302 may tapertoward one another so that the width of structure 310 in proximity toproximal end 31P is less than the width in proximity to distal end 31D.

According to some embodiments, shaft 510 of tool 500 is formed by atubular member, for example, which is attached around a shank 533 ofholding member 530, as shown in FIG. 4A. FIG. 4A further illustratesinsulation body 210 of device assembly 300 extending within shaft 510 oftool 500 so that connector assembly 215 extends proximally therefrom.But, in some alternate embodiments, insulation body 210 may extendalongside delivery tool shaft 510.

According to an exemplary embodiment, shaft 510 of delivery tool 500,for example, extending over a length of approximately 30 cm to 35 cm,may be formed by a stainless steel braid-reinforced medical gradepolymer of one or more appropriate grades of polyether block amide(e.g., PEBAX® 6333 and 7033); and holding member 530 of tool 500 may beformed from an appropriate grade of polyether block amide (e.g., PEBAX®7233) and include a radiopaque marker bonded thereto, for example, aPlatinum/Iridium or gold marker, or a polyamide material with aradiopaque filler, such as Tungsten-filled Vestamid®.

FIG. 5 is a schematic showing holding member 530 of delivery tool 500having been positioned in the pericardial space, via sub-xiphoid access,so the operator can secure electrode 32 of device assembly 300 at theepicardial site, for example, to provide pacing stimulation. FIG. 5illustrates a guiding sheath 700 providing a passageway for theinsertion of delivery tool 500 into the pericardial space, betweenepicardial surface 6 and pericardial sac 15, through access site A,which may be formed by any suitable method known in the art, forexample, as described above in conjunction with FIG. 1. Fluoroscopic orvideo monitoring may be employed for guidance in positioning holdingmember 530. Alternately, the operator may gain access to the pericardialspace, to position holding member 530 and assembly 300, via athoracotomy by methods known in the art. According to some methods,after positioning holding member 530 and device assembly 300 at theepicardial site, the operator applies a push force to mounting structure310 through an elongate stiffener 24 that extends in sliding engagementwithin insulation body 210 of device assembly 300, per arrow P, therebymoving device assembly 300 distally relative to delivery tool holdingmember 530 and releasing fixation tines 341, 342 to penetrate intotissue at the epicardial site. Then, the operator can retract tool 500from the pericardial space and withdraw stiffener 24 from deviceassembly 300. According to some alternate embodiments and methods, andwith reference back to FIG. 4A, the operator can apply the push force tomounting structure 310 through an optional ejector rod 54 of theinterventional medical system, which extends in sliding engagementwithin tool shaft 510.

FIG. 6 is a schematic depicting the release of fixation tines 341,according to some embodiments. In FIG. 6, positions of tines 341, 342,which are illustrated with dashed-line representations, correspond to atrajectory of tine release, per arrow R, for penetration of tinepiercing tips 40 into tissue. The solid line representation of tines341, 342 generally corresponds to full engagement thereof with tissue,which secures electrode 32 to the epicardial stimulation site. Anapproximate penetration depth BD of tines 341, 342 may be about 0.132inch (3.3 mm), as dictated by the above disclosed exemplary radius andlengths of tine portions 4V-2 and 4V-3 (FIG. 3A).

In the foregoing detailed description, the invention has been describedwith reference to specific embodiments. However, it may be appreciatedthat various modifications and changes can be made without departingfrom the scope of the invention as set forth in the appended claims.

1. An implantable medical device assembly comprising: a mountingstructure having a length defined from a proximal end thereof to adistal end thereof, a width defined from a first side thereof to asecond side thereof, and a surface that extends along the length andacross the width; an electrode protruding from the surface of themounting structure at a location offset proximally from the distal endof the structure, and approximately centered between the first andsecond sides of the structure; and first and second tissue-penetratingfixation tines, each tine including a pre-formed V-shaped segment thatextends away from the surface of the mounting structure, the segment ofthe first tine extending from the surface at a location adjacent to boththe first side and the distal end of the structure, the segment of thesecond tine extending from the surface at a location adjacent to boththe second side and the distal end of the structure, each segmentincluding a piercing tip, and each segment being elastically deformablefrom a relaxed condition to an extended condition, the relaxed conditionbeing that of the pre-formed V-shape, in which each segment extendstoward the proximal end and the surface of the mounting structure sothat each piercing tip is located adjacent to the electrode, and theextended condition being that in which each segment extends distallyaway from the distal end of the mounting structure so that each piercingtip is located distal to the distal end of the structure.
 2. Theassembly of claim 1, wherein: the mounting structure further comprisesfirst and second channels extending lengthwise, the first channel beinglocated adjacent to the first side of the structure and the secondchannel being located adjacent to the second side of the structure; andeach fixation tine further includes another segment extending in acorresponding channel of the first and second channels of the mountingstructure.
 3. The assembly of claim 2, wherein the other segment of eachfixation tine comprises an L-shaped segment.
 4. The assembly of claim 1,further comprising another electrode mounted to mounting structure forbipolar function with the electrode that protrudes from the surface ofthe mounting structure.
 5. The assembly of claim 1, further comprising:an elongate insulation body joined to the mounting structure andextending distally therefrom; another electrode mounted to the elongateinsulation body; and an elongate conductor coupled to the electrode andextending therefrom within the insulation body.
 6. The assembly of claim1, wherein: each fixation tine has a generally rectangular axialcross-section, the axial cross-section being uniform along the bothsegments of the tine, sans the piercing tips, and longer sides of eachaxial cross-section being orthogonal to a single plane in which bothsegments of each tine bend; and each fixation tine is oriented so thatone of the longer sides of the axial cross section thereof facesgenerally toward the surface of the mounting structure, when thepre-formed V-shaped segment is in the relaxed condition, and facesgenerally away from the surface of the mounting structure, when thepre-formed V-shaped segment is deformed into the extended condition. 7.The assembly of claim 6, wherein the piercing tip of each fixation tineincludes an angled surface, the angled surfaces facing generally towardone another.
 8. The assembly of claim 1, wherein the first and secondsides of the mounting structure taper toward one another so that thewidth of the structure in proximity to the proximal end of the structureis less than the width of the structure in proximity to the distal endof the structure.
 9. The assembly of claim 1, further comprising: anelongate conductor coupled to the electrode and extending therefromwithin the mounting structure to the proximal end thereof and proximallytherefrom; and an elongate insulation body joined to the mountingstructure and extending proximally therefrom, the body extending aroundthe conductor to provide electrical isolation thereof.
 10. Aninterventional medical system comprising: an implantable medical deviceassembly comprising: a mounting structure having a length defined from aproximal end thereof to a distal end thereof, a width defined from afirst side thereof to a second side thereof, and a surface that extendsalong the length and across the width; an electrode protruding from thesurface of the mounting structure at a location offset proximally fromthe distal end of the structure, and approximately centered between thefirst and second sides of the structure; and first and secondtissue-penetrating fixation tines, each tine including a pre-formedV-shaped segment that extends away from the surface of the mountingstructure, the segment of the first tine extending from the surface at alocation adjacent to both the first side and the distal end of thestructure, the segment of the second tine extending from the surface ata location adjacent to both the second side and the distal end of thestructure, each segment including a piercing tip, and each segment beingelastically deformable from a relaxed condition to an extendedcondition, the relaxed condition being that of the pre-formed V-shape,in which each segment extends toward the proximal end and the surface ofthe mounting structure so that each piercing tip is located adjacent tothe electrode, and the extended condition being that in which eachsegment extends distally away from the distal end of the mountingstructure so that each piercing tip is located distal to the distal endof the structure; a delivery tool comprising: an elongate shaftextending from a proximal end thereof to a distal end thereof; and aholding member attached to the distal end of the shaft, the holdingmember including first and second longitudinally extending sidewallsspaced apart from one another to receive passage of the device assemblymounting structure therebetween, each sidewall extending over a lengthdefined from a proximal end thereof to a distal end thereof, and eachsidewall including a rail-like edge extending along the length, eachrail-like edge being sized to receive in engagement therewith, and toelastically deform the segment of a corresponding fixation tine from therelaxed condition to the extended condition, when the proximal end ofthe mounting structure, with the surface of the mounting structurefacing toward the rail-like edges, is passed between the holding membersidewalls of the tool, from the distal ends of the sidewalls to theproximal ends of the sidewalls and proximally beyond; and means forapplying a push force to the mounting structure, when the distal end ofthe structure is located between the holding member sidewalls of thedelivery tool.
 11. The system of claim 10, wherein the delivery toolholding member further comprises means for engaging the device assemblymounting structure in proximity to the proximal end thereof, when thedistal end of the structure is located between the holding membersidewalls, to prevent the distal end of the mounting structure frompassing proximally out from between the holding member sidewalls. 12.The system of claim 11, wherein the means for engaging the deviceassembly mounting structure in proximity to the proximal end thereofcomprises a first stop member extending proximally from the proximal endof the first sidewall and a second stop member extending proximally fromthe proximal end of the second sidewall, the first and second stopmembers being oriented to abut the first and second sides of the deviceassembly mounting structure, when the distal end of the structure islocated between the holding member sidewalls.
 13. The system of claim10, wherein the implantable medical device assembly further comprises:an elongate conductor coupled to the electrode and extending therefromwithin the mounting structure to the proximal end thereof and proximallytherefrom; and an elongate insulation body joined to the mountingstructure and extending proximally therefrom, the body extending aroundthe conductor to provide electrical isolation thereof.
 14. The system ofclaim 13, wherein the means for applying the push force comprises anelongate stiffener sized to fit in sliding engagement within theinsulation body.
 15. The system of claim 10, wherein the means forapplying the push force comprises an ejector rod that extends in slidingengagement within the elongate shaft of the delivery tool.
 16. Atissue-penetrating tine component for an implantable medical deviceassembly, the component being formed from a super-elastic wire having agenerally rectangular axial cross-section uniform along a lengththereof, and the component comprising: a pre-formed L-shaped segmentextending from a first end to a second end; and a pre-formed V-shapedsegment extending from the second end of the L-shaped segment, theV-shaped segment including a piercing tip; and wherein a single plane inwhich both segments bend is orthogonal to longer sides of the axialcross-section; and the segments bend toward one another.
 17. Thecomponent of claim 16, wherein the pre-formed V-shaped segment bendsaround a radius of about 0.03 inch and includes a straight length ofabout 0.12 inch extending from the piercing tip.
 18. The component ofclaim 16, wherein the piercing tip comprises only two angled surfaces, afirst of the two being cut in one of the longer sides of the axialcross-section and a second of the two being cut in a shorter side of theaxial cross-section.
 19. A method for securing an electrode to anepicardial site, the electrode protruding from a surface of a mountingstructure of an implantable device assembly, and the method comprising:passing a proximal end of a mounting structure of the assembly betweenopposing longitudinally extending sidewalls of a holding member of adelivery tool, at distal ends of the sidewalls, and with a surface ofthe structure, from which the electrode protrudes, facing towardrail-like edges of the sidewalls, the holding member being attached to adistal end of an elongate shaft of the delivery tool; continuing to passthe proximal end of the mounting structure from the distal ends of theopposing sidewalls of the holding member to proximal ends of theopposing sidewalls and proximally beyond the proximal ends of thesidewalls until a distal end of the mounting structure is locatedbetween the proximal ends of the sidewalls and the rail-like edgeselastically deform tissue-penetrating fixation tines of the deviceassembly from a relaxed condition to an extended condition, eachfixation tine extending away from the surface of the mounting structure,the relaxed condition of each tine being that in which each tine extendstoward the proximal end and the surface of the mounting structure, andthe extended condition of each tine being that in which each tineextends distally away from the distal end of the mounting structure;positioning the holding member and the device assembly with the tinesthereof in the extended condition at the epicardial site; and releasingthe fixation tines of the device assembly from the extended condition toengage with tissue at the site by applying a push force to the mountingstructure of the device assembly.
 20. The method of claim 19, whereinthe push force is applied through an elongate stiffener extending insliding engagement within an insulation body of the device assembly, theinsulation body being joined to the mounting structure and extendingproximally therefrom.
 21. The method of claim 19, wherein the push forceis applied through an ejector rod that extends in sliding engagementwithin the tool shaft.